The present invention relates to an automatic cooking control system for a microwave oven which automatically cooks a food contained in a heating chamber by utilizing temperature detecting sensors. More specifically, the present invention relates to an automatic cooking control system for a microwave oven which is allowed to cook by correctly establishing a heating period of time for a food even if foods are successively cooked. In other words, when a microwave oven is being utilized again after a first portion of food is cooked to immediately cook another portion of food.
A conventional microwave oven, as shown in FIG. 1, with a microcomputer 1 which controls the whole operation of a microwave oven; a power source 2 which supplies the electric power according to the control of the microcomputer, a magnetron 3 which generates microwave energy upon being actuated by an output of electric power from the power source 2, a heating chamber 4 which heats food with the microwave energy generated from the magnetron 3; a fan 5 which blows an air through an air inlet 4A into the heating chamber 4; a temperature detecting sensor 6 which detects a temperature of an air flowed out through an air outlet 4B of the heating chamber 4; an analog/digital converter 7 which converts a temperature signal of the outflow air detected by the temperature detecting sensor 6 into a digital signal and supplies the digital signal to the microcomputer 1.
The conventional microwave oven as described above, when a user begins the cooking process by putting a food to be cooked into the heating chamber 4 starts the cooking cycle by pressing a cooking start button. The microcomputer 1 performs an initial operation for a predetermined period of time t.sub.1, as shown in FIGS. 2 and 3. During this period, the air temperature of the heating chamber 4 is made uniformed by blowing an air into the heating chamber 4 through an air inlet 4A. This is achieved by actuating a fan 5 for about sixteen seconds, a temperature of the air flowing out through an outlet 4B of the heating chamber 4 is detected by a temperature detecting sensor 6. Then the detecting temperature signal is converted into a digital signal by an analog/digital converter 7.
When a predetermined period of time t.sub.1 has elapsed, the microcomputer receives and stores a signal representing the presently existing temperature T.sub.1 which has been outputted from the analog/digital converter 7. Thereafter, the microcomputer 1 actuates a magnetron 3 by controlling a power source 2. When the magnetron 3 is actuated, the magnetron 3 is allowed to heat the food contained in the heating chamber 4 by generating microwave energy. The temperature of the air flowing through the air outlet 4B of the heating chamber 4 is gradully raised in accordance with the heating of the food; therefore, a temperature detection signal which is inputted to the microcomputer 1 through the analog/digital converter 7 is gradually raised.
When the air temperature is raised an increment that is equal to a predetermined value .DELTA.T, that is when the temperature detected at a temperature detecting sensor 6 is raised to a predetermined temperature T2, the microcomputer 1 finishes a first stage heating process and starts to execute a second stage heating process a period of time t.sub.2 to execute a first stage heating process is stored. A second stage heating period of time t.sub.3 is then calculated by multiplying a predetermined value .alpha. established in accordance with the kind of food being cooked with the period of time t.sub.2. The food is heated by continuously actuating the magnetron 3 during the second stage heating for period of time t.sub.3. When the second stage heating proces period of time t.sub.3 is elapsed, the operation of a magnetron 3 and a fan 5 is halted, and the cooking of the food is completed.
However, in the conventional automatic cooking control system, as described above, when another food is cooked immediately under after a microwave oven has been used to heat an initial food portion, the automatic cooking of the food cannot be readily accomplished because the temperature increasing rate becomes non-existent relative to the increasing rate realized during the cooking of the initial food portion.
As shown in FIG. 4A, when cooking another food at a temperature T.sub.4, T.sub.5, T.sub.6, T.sub.7, or T.sub.8 that is higher than a normal temperature T.sub.1, the air temperature at an air outlet 4B which is detected by the temperature detecting sensor 6 is raised to a predetermined temperature T.sub.3. Thereafter, the air temperature is gradually cooled, as shown in FIG. 4B. Since a first stage heating period and a second stage heating period will become longer when the temperature increasing rate decreases in accordance with the condition that a starting cooking temperature is still high, the food is over heated. This situation causes a disadvantage in that a food can only be automatically cooked when at least 10-30 minutes have elapsed after the initial food is cooked.